1. Field of the Invention
The present invention relates to indexable inserts. More particularly, the present invention relates to apparatus for providing thread forms on a workpiece and apparatus for turning a workpiece. Still more particularly, the present invention relates to a threading and turning insert which is indexable and integrally incorporates a pressed-in chip breaker, respectively, for each of the threading and turning insert portions thereof.
2. Description of the Related Art
Threading of a workpiece is conventionally performed using a positive, precision ground fiat-face threading insert. The conventional threading insert is presented in a neutral position to the centerline of the workpiece, which requires that the conventional threading insert have a positive clearance angle. This positive geometry limits the number of cutting edges to just one. The conventional threading insert is used in conjunction with an adjoining, separate, inclined surface mechanical chip breaker. The conventional threading insert and mechanical chip breaker are seated in a pocket of a toolholder for providing selected engagement with respect to a workpiece to thereby provide it with threads.
While the conventional threading insert performs its thread cutting function adequately, there yet remains the problem that when the conventional threading insert cutting edge becomes dull or otherwise unacceptable, the threading insert must be replaced with a new or resharpened one.
Conventional mechanical chip breakers are ground in the form of an inclined plane, having a pointed edge adjacent the cutting edge of the threading insert, inclining increasingly with increasing distance from the cutting edge of the threading insert, and terminating in a planar face. The conventional mechanical chip breaker produces very long, razor-like, wiry chips which can damage the threading insert, the toolholder, the workpiece, or the operator. Further, these chips are difficult to collect and pose disposal handling problems. Still further, the optimum position of the conventional mechanical chip breaker with respect to the cutting edge of the threading insert is almost impossible to consistently achieve. As a result, material build-up between the mechanical chip breaker and the threading insert can be expected to occur. This build-up ultimately can cause poor part finish, premature insert failure, and even possible insert breakage.
It is ideal for the workpiece to be broken into manageable chips in the form of "C's" and "9's" which are narrower than the threads being formed. Narrowing the removed material helps to initiate chip control by bending the material away from the sides of the thread grooves, thereby concentrating the stress and strain properties of the material toward the center of the chips. Thus, the prior art chip breaker suffers from being deficient in chip management.
The ability of pressing a chip breaker form onto a positive threading insert is very difficult. When pressing into a positive die cavity, a neutral press land cannot be avoided when the green insert is ejected. A neutral press land prevents the insert from having a positive edge at the intersection of the insert's rake face. Pressing a positive insert without the appearance of a press land presents a major problem with current manufacturing techniques.
Cutting inserts for turning a workpiece are known in the art, such as for example an indexable insert disclosed in U.S. Pat. No. 5,249,894. Turning is frequently a part of the over-all machining operation associated with the fabrication of a threaded workpiece. For example, a taper may be provided on the workpiece prior to execution of the threading operation. It remains a problem in the art to devise an insert which takes into account a systems approach to machining of a workpiece when both turning and threading operations are involved.
Accordingly, what remains needed in the art is a threading and turning insert which is indexable and provided with an integral chip breaker, respectively, for each of the threading and turning insert portions thereof.